THE STRUCTURAL BASIS OF THE BODY 



31 



In order to appreciate the part played by the nucleus in the ordinary 

 cell processes, we must study the behaviour of cells or parts of cells 

 deprived of a nucleus and compare it with that of similar cells or 

 parts of cells still containing a nucleus. By means of a fine needle it is 

 possible to divide the larger protozoa into two pieces, one with and 

 one without a nucleus. Hofer, experimenting on the amoeba, found 



A 



FIG. 9. Regeneration in the unicellular animal Stentor. (From GRTJBER after 



BALBIANI.) 



A. Animal divided into three pieces, each containing a fragment of the nucleus. 

 B. The three fragments shortly afterwards. C. The three fragments after twenty- 

 four hours, each regenerated to a perfect animal. 



that the fragment containing the nucleus quickly regenerated the 

 missing part and pursued a normal existence. On the other hand, the 

 non-nucleated fragments showed no signs of regeneration. They might, 

 indeed, live as long as fourteen days after the operation (Fig. 8). Their 

 movements continued for a short time and then ceased, though the 

 pulsations of the contractile vesicle were but little affected. The power 

 of digestion of food was completely lost. Other observers have shown 

 that Stentor, an infusorium which possesses a fragmented nucleus, 

 may be broken up into fragments of all sizes. Nucleated fragments as 

 small as one-twenty-seventh the volume of the entire animal are still 

 capable of regeneration. The wound quickly heals and the special 

 organs the mouth, with its surrounding cilia, and the contractile 



